Two new railway axes under construction through the Swiss Alps will provide a vital link between the high speed rail networks of Germany and Italy, and in the process bring a reduction in the heavy road traffic – a key factor for the Swiss government in giving approval.
The $17bn AlpTransit Scheme (NEAT) includes two major tunnels; the 57km long Gotthard Base Tunnel (GBT) and the Lötschberg Base Tunnel (LBT) at 35km. Both comprise two parallel single track tubes connected by cross galleries, and are excavated by TBM or drill and blast. Several access galleries divide the two main tubes into different sections, to reduce construction time.
Gotthard Base Tunnel
The GBT is divided into Bodio, Erstfeld, Amsteg, Sedrun and Faido sections, the last three connected with an intermediate drive on the surface.
Most excavation is by TBM or drill and blast. Only Sedrun has to be done with conventional drive because of the complex geology.
The Sedrun section is the most complex of the whole project as it involves penetrating the northern part of the Tavetsch intermediate massif. The planned method of dealing with the anticipated squeezing conditions is based on a full-face excavation with systematic securing of the face, the installation of deformable steel arches together with a radial rock bolting system. The lot will be awarded in December 2001.
Due to costs and time schedule the two main lots of Faido and Bodio have been combined, in an $823M award made in June 2001 to the TAT JV. Two 8.8m diameter Herrenknecht open hard rock TBMs will start in Bodio next October and end at the southern end of the Sedrun section.
The most difficult zone will be the Piora Basin. Here to cope with the defomations caused by the squeezing, the cutterhead will overcut by 300mm to create extra space.
The multi-functional station (emergency train stops) and the track changes are excavated by drill and blast with slurry.
The contract for the Amsteg section is expected to be awarded this month. Tender documents leave excavation method to time and cost, with both TBM drive or conventional method an option. Tendering for Erstfeld is planned for 2002/2003.
Lötschberg Base Tunnel
The two main LBT tubes are packaged into sections; Mittholz with one tube to the north and two to the south, Ferden with two drives to the north and south, Steg, Raron and Frutigen.
The Frutigen and Mitholz sections are excavated by drill and blast after the high cost of a TBM drive from Mitholz ruled it out. A TBM heading for the tubes towards the south was also dropped by the client for safety reasons – high underground water pressures and the possible presence of karst water.
However a Herrenknecht TBM has been operating in the Steg access heading since mid-2000, and a second started at Raron in the middle of this year for the same joint venture, MaTrans. Both are modern open hard rock machines, applying the latest “innovative safety concept” during constructing.
The Ferden section, where work started in May, includes the drill and blast operations for the two base tunnel drives from the access gallery base point in the direction of Valais (south) and towards Bern (north).
Stage of work – GBT
Construction on the 1.2km long access gallery in Amsteg began in June 1999 and is now complete. The first contract was extended to include preparatory work at the point were the access tunnel joins the two single tracks of the base tunnel. There a cavern with a maximum excavated cross-section of 195m2 has created a 90m chamber for the subsequent rail technical installations, an assembly cavern for the future mechanised drives, a total of 360m of single track tube and a crosscut. This work was finished in February 2001.
The joint venture bid for the main contract was tabled in March 2001 and award is expected at the end of the year. Meanwhile, work at the Amsteg section has been interrupted.
The excavation at Sedrun started in April 1996 with the access gallery, followed in autumn 1998 by the shaft, then by the longitudinal cavern one and the cross-caverns one and two. Excavation and concrete lining of the shaft bottom caverns is also complete. The shaft haulage installation will go into service for the main section in autumn 2002. Main contract will be awarded at the end of 2001.
Construction work for the access gallery in Faido started in December 1999 after initial work on the underpass for the cantonal road. Excavation is now concluded, while the concrete lining work continues. The lot was extended by about 55m to prepare the excavation of the cross cavern ahead of the main lot.
Along with driving operations for the access gallery, material management was tackled with one lot for a dump in Cavienca and another for a preparation plant and a 4.9km long conveyor belt, leading to the dump. The contract for the main lot will be awarded shortly, as will the main lot of Bodio. The work on the installation area starts in December and excavation of the multi-functional station and the main tubes in March next year.
In Bodio, over half of the 400m long cut-and-cover section has been completed. A conveyor system takes excavated material to the neighbouring Blenio valley where it is deposited. A part of the conveyor belt leads through a mucking gallery which was excavated by TBM and completed in April 2001. A bypass heading to surround the cut-and-cover section was completed in summer 2001. The portal cut and the soft ground penetration is still in progress. The main lot has been awarded to the joint venture TAT in combination with the main lot of Faido.
The last main lot in Erstfeld will not be started before 2003.
Stage of work – LBT
Currently, nine sections are being driven on the Lötschberg Base Tunnel. (T&TI, October 2000) On the Bern side, the drives are progressing according to schedule. Already as much as 5,800m of tunnel have been excavated at the northern end of the base tunnel.
At the Mitholz bottom point, a test section is being developed in a side tunnel. This is to gain experience and eliminate any possible problems prior to the main drive, enabling installation to be optimised. This applies to issues concerning maintenance as well as rail technical furnishings.
At the Valais side, the planned hand over between joint ventures at Ferden from the access tunnel work to the main base tunnel section took place in May 2001.
The joint venture now responsible for the Ferden main contract section has started driving operations, and is in parallel setting up installations for four drives. In the Steg access tunnel, the gripper TBM is now penetrating the hardest rock (granodiorite) after initially achieving peak rates.
The second TBM has been assembled at the Raron portal and started operating this summer.
Outlook
The main contracts at the Lötschberg Base Tunnel have already started, while the main lots at the Gotthard Base Tunnel are set to begin towards the end 2002, with the northern lot in Erstfeld following in 2003.
According to the schedule, it should be possible to complete tunnelling work at Lötschberg by mid-2004 and Gotthard in 2010. On current progress, the Lötschberg Base Tunnel should open at the end of 2006 or the beginning of 2007 with the Gotthard Base Tunnel coming on stream in 2012.
Related Files
Lötschberg techniques
Switzerland
Plan diagram of the Gotthard tunnel
3D Image of Gottard tunnel